A hemoglobin test measures the amount of hemoglobin in your blood. Hemoglobin is a protein in your red blood cells that carries oxygen to your body's organs and tissues and transports carbon dioxide from your organs and tissues back to your lungs.
If a hemoglobin test reveals that your hemoglobin level is lower than normal, it means you have a low red blood cell count (anemia). Anemia can have many different causes, including vitamin deficiencies, bleeding and chronic diseases.
If a hemoglobin test shows a higher than normal level, there are several potential causes — the blood disorder polycythemia vera, living at a high altitude, smoking and dehydration.
You may have a hemoglobin test for several reasons:
If your blood sample is being tested only for hemoglobin, you can eat and drink normally before the test. If your blood sample will be used for other tests, you may need to fast for a certain amount of time before the sample is taken. Your doctor will give you specific instructions.
For a hemoglobin test, a member of your health care team takes a sample of blood by pricking your fingertip or inserting a needle into a vein in your arm. For infants, the sample may be obtained by pricking the heel.
The blood sample is sent to a lab for analysis. You can return to your usual activities immediately after the sample is taken.
The normal range for hemoglobin is:
Normal ranges for children vary with age and sex. The range for a normal hemoglobin level may differ from one medical practice to another.
If your hemoglobin level is lower than normal, you have anemia. There are many forms of anemia, each with different causes, which can include:
If you've been previously diagnosed with anemia, a hemoglobin level that's lower than normal may indicate a need to alter your treatment plan.
If your hemoglobin level is higher than normal, it may be the result of:
If you've been previously diagnosed with polycythemia vera, an elevated hemoglobin level may indicate a need to alter your treatment plan.
If your hemoglobin level is below or above normal, your doctor may want to evaluate the hemoglobin test results along with those of other tests, or additional tests may be necessary, to determine next steps.
For specifics about what your hemoglobin test results mean, talk to your doctor.